This excerpt taken from the PBI DEF 14A filed Mar 23, 2006.
Any eligible employee who applies for an option under the SAYE Plan must enter into a save as you earn contract approved by the U.K. H M Revenue and Customs (the Savings Contract) with an authorized financial institution. The option holder agrees to make monthly savings by payroll deduction of a fixed amount, currently not less than £10 or more than £250 per month, and chooses either a three-year or a five-year savings period.
Upon expiration of the Savings Contract, the option holder will be entitled to a tax-free bonus in addition to repayment of the savings contributions. This bonus is the equivalent of further monthly contributions (in lieu of interest). The number of additional contributions is fixed by the U.K. Treasury.